1. Field of the Invention
The present invention relates to a high-density read-only optical information storage medium in which a pattern necessary for data reproduction is formed in a lead-in area and/or a lead-out area, thus improving reproduction characteristics, and a method of reproducing data from such a high-density read-only optical information storage medium.
2. Description of the Related Art
Generally, information storage media such as, for example, optical disks, are widely used in optical pickup apparatuses for recording/reproducing information in a non-contact way. Optical disks are classified as compact disks (CDs) or digital versatile disks (DVDs) according to their information storage capacity. Examples of recordable optical disks include 650 MB CD−R, CD−RW, 4.7 GB DVD+RW, DVD−RAM (random access memory), and DVD−R/RW (rewritable). Furthermore, HD-DVDs having a recording capacity of 20 GB or greater are under development.
As the capacity of information storage media increases as described above, the length and width of a pit recorded on read-only information storage media decrease. With such a reduction of the pit length and pit width, a signal for a minimum mark becomes very small, which makes it more difficult to measure a modulation degree. The modulation degree measurement is needed to measure the recording and/or reproduction performance of a data signal. For example, the degree of modulation based on a run-length-limited RLL (d, k) modulation technique is I(d+1)/I(k+1), wherein I denotes the intensity of a signal in an eye pattern. The eye pattern is a graph showing the characteristics of a data signal.
In a run-length-limited (RLL) modulation technique, modulation is performed based on how many bits of a value 0 exist between two bits of a value 1. RLL (d,k) represents that the minimum and maximum numbers of bits of 0 between two bits of 1 are d and k, respectively. For example, RLL (1,7) represents that the minimum and maximum numbers of bits of 0 between two bits of 1 are 1 and 7, respectively. In an RLL (1,7) modulation technique, if one bit of 0 exists between two bits of 1, data “1010101” is recorded. Hence, a length between two bits of 1 is 2T. If 7 bits of 0 exist between two bits of 1, data “10000000100000001” is recorded, and accordingly, a length between two bits of 1 is 8T. Here, T denotes the length of a minimum mark, that is, a minimum pit. Hence, in the RLL (1,7) modulation technique, data is recorded in the form of pits and spaces that range in length between 2T and 8T.
In an RLL (2,10) modulation technique, data is recorded in the form of pits and spaces that range in length between 3T and 11T.
In the RLL (1,7) modulation technique, a modulation degree is measured as I2/I8. In the RLL (2,10) modulation method, a modulation degree is measured as I3/I11.
FIG. 1 shows a structure of a lead-in area of a conventional read-only information storage medium. The lead-in area includes a control data zone 100a, a buffer zone 100b, and information zone 100d. The control data zone 100a stores disc-related information and copy protection information. The information zone 100d stores information regarding the state of a driver or disc. The lead-in area further includes a reserved zone 100c to store data that has not yet been determined but is added later.
As shown in FIG. 1, the conventional read-only information storage medium does not include an area used to measure a modulation degree. Accordingly, a measurer must measure a modulation degree directly from the eye pattern of data recorded in a user data area.
FIG. 2 shows an eye pattern for a random signal during data recording based on the RLL (1,7) modulation technique. In FIG. 2, the horizontal axis denotes the time, and the vertical axis denotes the intensity (I) of a signal. In the related art, when a modulation degree is measured using such an eye pattern as shown in FIG. 2, a measurer moves the cursor of an oscilloscope to a crest of the wave of a signal pattern corresponding to a 2T-long minimum pit in order to measure I2, and also moves the cursor of the oscilloscope to a crest of the wave of a signal pattern corresponding to an 8T-long maximum pit in order to measure I8, thereby measuring a modulation degree of I2/I8.
However, with an increase in the recording capacity of information storage media, the length and width of a minimum pit decrease, and hence, the eye pattern of the minimum pit becomes smaller and, in turn, more difficult to accurately measure. Thus, in such a conventional modulation degree measuring technique, different measurers may output different measurement results, thus increasing an error. In other words, as the amplitude of an eye pattern decreases, measurers are increasingly likely to move an oscilloscope cursor to different locations on a crest of the wave of a signal pattern corresponding to the length of a minimum pit. Thus, the accuracy of a measured modulation degree is degraded. This problem becomes more serious as the capacity of information storage media increases. Also, as the length of a space between adjacent pits decreases, serious cross-talk occurs, which impedes an accurate measurement of a modulation degree.
The above-described modulation degree measurement is necessary upon data reproduction. A system adaptation process is also necessary upon data reproduction. These requisites for data reproduction must be satisfied to achieve smooth data reproduction.